Generate a MKCoordinateRegions for continents and major oceans

MapRegionUtility.swift

  //
  //  MapRegionUtility.swift
  //  QuakeData
  //
  //  Created by Adrian Bolinger on 7/9/18.
  //  Copyright © 2018 Adrian Bolinger.
  //
  /*
  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   */

  import UIKit
  import MapKit

  class BoundingBox: NSObject {
    let min: CLLocationCoordinate2D
    let max: CLLocationCoordinate2D
    
    init(mapRect: MKMapRect) {
      let bottomLeft = MKMapPointMake(mapRect.origin.x, mapRect.origin.y)
      let topRight = MKMapPointMake(MKMapRectGetMaxX(mapRect), MKMapRectGetMaxY(mapRect))
      
      self.min = MKCoordinateForMapPoint(bottomLeft)
      self.max = MKCoordinateForMapPoint(topRight)
      super.init()
    }
    
    init(displayRegion: GeographicRegion) {
      let coordinateArray = displayRegion.rawValue.components(separatedBy: ",").map{Double($0)!}
      min = CLLocationCoordinate2D(latitude: coordinateArray[3], longitude: coordinateArray[2])
      max = CLLocationCoordinate2D(latitude: coordinateArray[1], longitude: coordinateArray[0])
      super.init()
    }
  }

  enum GeographicRegion: String {
    
    /*
     Where'd these numbers come from?
     1) go to https://boundingbox.klokantech.com
     2) In "Find Place With Google", type whatever you want a bounding box for
     3) Select "CSV RAW" and copy.
     
     Copied format is as follows:
     
     bbox = minLongitude , minLatitude , maxLongitude , maxLatitude
     
     Don't like the spans? Feel free to change them at the site above
     
     */
    
    case asia = "25.5886467,-12.2118513,-168.97788,81.9661865"
    case africa = "-25.383911,-47.1313489,63.8085939,37.5359"
    case northAmerica = "-172.66113495,5.4961,-15.51269745,83.6655766261"
    case southAmerica = "-110.0281,-56.1455,-28.650543,17.6606999"
    case antarctica = "-180.0,-85.0511287798,180.0,-60.1086999"
    case europe = "-25.48824365,32.5960451596,74.3555001,73.1927977675"
    case australia = "110.9510339,-54.8337658,159.2872223,-9.1870264"
    
    case pacificOcean = "128.576489,-77.8225785,-66.5190814,59.4822293"
    case atlanticOcean = "-83.2160952,-83.0204773,20.0000002,68.6187516"
    case indianOcean = "13.0882271,-61.8516375745,146.9166667,25.9666428755"
    case antarcticOcean = "-160.2500533,-68.4421138,-160.2180385,-68.4339125"
    case arcticOcean = "-68.9751267,62.8298713,-55.6975281,67.708443"
  }


  class RegionUtility: NSObject {
    
    public func region(for region: GeographicRegion) -> MKCoordinateRegion {
      return MKCoordinateRegion(coordinates: bboxCoordinates(from: region.rawValue))!
    }
    
    private func bboxCoordinates(from coordinateString: String) -> [CLLocationCoordinate2D] {
      var coordinateArray: [CLLocationCoordinate2D] = []
      let boundingBoxArray: [Double] = coordinateString.components(separatedBy: ",").map{Double($0)!}
      
      let max = CLLocationCoordinate2D(latitude: boundingBoxArray[1], longitude: boundingBoxArray[0])
      let min = CLLocationCoordinate2D(latitude: boundingBoxArray[3], longitude: boundingBoxArray[2])
      coordinateArray = [min, max]
      
      return coordinateArray
    }
  }

  extension MKCoordinateRegion {
    
    // From: https://gist.github.com/dionc/46f7e7ee9db7dbd7bddec56bd5418ca6
    init?(coordinates: [CLLocationCoordinate2D]) {
      
      // first create a region centered around the prime meridian
      let primeRegion = MKCoordinateRegion.region(for: coordinates, transform: { $0 }, inverseTransform: { $0 })
      
      // next create a region centered around the 180th meridian
      let transformedRegion = MKCoordinateRegion.region(for: coordinates, transform: MKCoordinateRegion.transform, inverseTransform: MKCoordinateRegion.inverseTransform)
      
      // return the region that has the smallest longitude delta
      if let a = primeRegion,
        let b = transformedRegion,
        let min = [a, b].min(by: { $0.span.longitudeDelta < $1.span.longitudeDelta }) {
        self = min
      }
        
      else if let a = primeRegion {
        self = a
      }
        
      else if let b = transformedRegion {
        self = b
      }
        
      else {
        return nil
      }
    }
    
    // Latitude -180...180 -> 0...360
    private static func transform(c: CLLocationCoordinate2D) -> CLLocationCoordinate2D {
      if c.longitude < 0 { return CLLocationCoordinate2DMake(c.latitude, 360 + c.longitude) }
      return c
    }
    
    // Latitude 0...360 -> -180...180
    private static func inverseTransform(c: CLLocationCoordinate2D) -> CLLocationCoordinate2D {
      if c.longitude > 180 { return CLLocationCoordinate2DMake(c.latitude, -360 + c.longitude) }
      return c
    }
    
    private typealias Transform = (CLLocationCoordinate2D) -> (CLLocationCoordinate2D)
    
    private static func region(for coordinates: [CLLocationCoordinate2D], transform: Transform, inverseTransform: Transform) -> MKCoordinateRegion? {
      
      // handle empty array
      guard !coordinates.isEmpty else { return nil }
      
      // handle single coordinate
      guard coordinates.count > 1 else {
        return MKCoordinateRegion(center: coordinates[0], span: MKCoordinateSpanMake(1, 1))
      }
      
      let transformed = coordinates.map(transform)
      
      // find the span
      let minLat = transformed.min { $0.latitude < $1.latitude }!.latitude
      let maxLat = transformed.max { $0.latitude < $1.latitude }!.latitude
      let minLon = transformed.min { $0.longitude < $1.longitude }!.longitude
      let maxLon = transformed.max { $0.longitude < $1.longitude }!.longitude
      let span = MKCoordinateSpanMake(maxLat - minLat, maxLon - minLon)
      
      // find the center of the span
      let center = inverseTransform(CLLocationCoordinate2DMake((maxLat - span.latitudeDelta / 2), maxLon - span.longitudeDelta / 2))
      
      return MKCoordinateRegionMake(center, span)
    }
  }